X-ray Excited Auger Electron Spectroscopy Research Articles

Chemical state and wettability of ion-irradiated diamond surfaces

It is shown that the wettability of diamond can be tailored in a broad range by the surface modification via ion bombardment. The polished MPCVD diamond films were oxidized in air at 550 °C to make the surface hydrophilic and then were irradiated with Ar + ions at 1 keV energy at doses ranging from 1×10 14 to 5×10 16 cm −2. The surface state evolution was monitored in situ with X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES). A progressive sp 3 to sp 2 bond transformation took place with the dose increase, while the irradiated surface becomes hydrophobic with the water contact angle increasing from 24° to 67° as measured with a sessile drop method. The heating of the ion-treated samples in air at 450 °C restores the hydrophilic properties inherent to oxidized diamond surface.

Characterization of hydrogenated diamond-like carbon films electrochemically deposited on a silicon substrate

Diamond-like carbon (DLC) films were deposited on a Si substrate by electrolysis in a methanol solution at ambient pressure and low temperature. The morphology and microstructure of the resulting DLC films were analysed using atomic force microscopy, Raman spectroscopy, Fourier transformation infrared spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray excited Auger electron spectroscopy (XAES). The surface energy and mechanical properties of the DLC films were examined, and the growth mechanism of the DLC films in liquid phase electro-deposition is discussed as well. The results of the study show that the hydrogenated diamond-like carbon films are smooth and compact. The percentage of sp3 carbon in the DLC films is determined as 55–60%, based on the corresponding XPS and first-derivative XAES spectra of graphite, diamond, and the tested films. The DLC films show low surface free energy, good mechanical properties, excellent friction–reduction and wear-resistance. It is suggested that methanol dissociates to generate the active species of and C2H4 at high voltage applied to the electrode, followed by the generation of the alkyl chain [–CH2–CH2–]n whose C–C and C–H bond lengths and C–C–C and H–C–H bond angles are close to that of diamond. Subsequently, a diamond-like structure was formed by the ordered dehydrogenation of a short-chain [–CH2–CH2–]n in the electrolysis process.

CVD of Nanosized ZnS and CdS Thin Films from Single-Source Precursors

A chemical vapor deposition (CVD) route to nanosized ZnS and CdS thin films was developed. The layers were deposited on substrates in a atmosphere at temperatures between 473 and 723 K using as single-source precursors. Thermal decomposition and fragmentation of compounds were investigated by thermal analyses and mass spectrometry. The sulfide films were thoroughly characterized in their composition, nanostructure, and morphology by means of several analytical techniques. Surface and in-depth chemical composition was studied by X-ray photoelectron spectroscopy, X-ray excited Auger electron spectroscopy, and secondary ion mass spectrometry. Film nanostructure and surface topography were investigated as a function of the synthesis conditions by glancing incidence X-ray diffraction and atomic force microscopy, respectively. Optical absorption properties were also studied. Nanophasic and contaminant-free ZnS and CdS thin films with an average crystallite size lower than 25 nm were obtained. The layers mainly contained the hexagonal (α) sulfide phase and displayed a smooth and regular surface morphology. In the present work, the influence of synthesis conditions on film characteristics is analyzed and discussed. © 2004 The Electrochemical Society. All rights reserved.

Nitrogen adsorption on supported size-selected tungsten nanoclusters as studied by X-ray photoelectron and X-ray excited Auger electron spectroscopies

Adsorption states of nitrogen on tungsten pentamers supported on a highly oriented pyrolytic graphite surface have been investigated using X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy. An adsorption state that is not seen on a bulk polycrystalline tungsten surface was observed at temperatures below room temperature. It has been found that the adsorption state is a molecular state and is a precursor to dissociation of N 2 on the tungsten nanocluster.

A sol–gel approach to nanophasic copper oxide thin films

Nanostructured copper oxide films were prepared via sol–gel starting from ethanolic solutions of copper (II) acetate [Cu(CH 3COO) 2·H 2O]. Films were obtained by dip-coating at room temperature in air and were subsequently heat-treated at different temperatures (100–900 °C) in oxidizing (air), inert (N 2) or reducing (4% H 2 in N 2) atmospheres. The evolution of the oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction, X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy. Different crystalline phases were observed as a function of the annealing conditions. Depending on both temperature and atmosphere, the film composition resulted single- or multi-phasic. All the layers were nanostructured with an average crystallite size lower than 20 nm. The most relevant results concerning sample composition and microstructure as well as their mutual relations with the synthesis conditions are presented and discussed.

Single‐Source Chemical Vapor Deposition of Zinc Sulfide‐Based Thin Films from Zinc bis(O‐ethylxanthate)

AbstractA novel single‐source precursor, zinc bis(O‐ethylxanthate), was employed for the CVD of ZnS‐based thin films. The coatings were deposited on SiO2 and SiO2/Si(100) substrates in a N2 atmosphere in a cold‐wall reactor in the temperature range 250–400 °C. The optical properties of the films were investigated by ultra violet‐visible (UV‐vis) absorption and Fourier transform infrared (FTIR) spectroscopies. The surface and in‐depth chemical composition were studied by X‐ray photoelectron spectroscopy (XPS), X‐ray excited Auger electron spectroscopy (XE‐AES), and secondary ion mass spectrometry (SIMS). Finally, atomic force microscopy (AFM) was employed to analyze the surface morphology of the coatings. Very thin films, with thickness less than 30 nm and no evidence of crystalline phases, were grown at temperatures of at least 300 °C. Optical measurement showed that the coatings were highly transparent ( > 80 %) throughout the visible and IR spectral ranges.

Active sites on an oxide catalyst for F/Cl-exchange reactions: X-ray spectroscopy of fluorinated γ-Al2O3

The dismutation of CHClF2 to CHF3 and CHCl3 was used to probe the effect of γ-Al2O3 fluorination on fluorine-against-chlorine (Cl/F) exchange reactions. X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES) and X-ray absorption near edge structure (XANES) spectroscopy were employed to probe the modifications at the surface of γ-Al2O3 accompanying the initial stages of fluorination. The results suggest that fluorine uptake by γ-Al2O3 starts initially at the surface of the oxide particles, with the formation of a fluorine species that is characterised by a single bond and a high effective charge q. Catalytic Cl/F-exchange is only observed after accumulation of higher fluorine concentrations, for which insertion of fluorine into the sub-surface region of the oxide crystallites has commenced. Quantitative XPS shows that the fluorination level must exceed approximately 10 atom% of the anions to achieve catalytic activity. The spectroscopic evidence suggests that the formation of aluminium oxofluorides is sufficient to provide catalytic activity. The presence of an AlF3 phase is not a condition for the observation of catalytic activity, even though defect-rich AlF3 is ultimately the endpoint of the fluorination process and is itself a Cl/F exchange catalyst.

X-ray absorption and photoemission electron spectroscopic investigation of crystalline and amorphous barium silicates

X-ray absorption near edge structure (XANES) measurements at the Si K-edge, X-ray photoelectron spectroscopy of the Si 2p and O 1s photoelectrons and X-ray excited Auger electron spectroscopy of the Si KLL Auger electrons are applied in order to investigate the degree of polymerisation (Q n ) of the (SiO 4)-polyhedra in barium silicate glasses with different BaO-contents. The spectra of the glasses with 33.3 and 37.0 mol% BaO are compared to those of the crystalline reference compounds: low quartz, BaSi 2O 5, BaSiO 3 and Ba 2SiO 4. The analysis reveals a high average polymerisation between Q 3 and Q 4 in both glasses. The results are supported by calculations of the bound state transitions in Si K-XANES using the multiple scattering Xα method.

Chemical and physical routes for composite materials synthesis: Ag and Ag2S nanoparticles in silica glass by sol–gel and ion implantation techniques

Two composite systems, “Ag” and “Ag–S” nanoparticles in silica films, were approached by using two different synthesis routes, namely sol–gel and ion implantation. Silica composites containing embedded nanosized silver- and silver sulfide-crystallites were obtained by the sol–gel process. The formation of silver nanograins was also observed in Ag-implanted silica samples, while sequential implantation (first Ag then S) led to the formation of core–shell Ag–Ag2S nanoclusters. The systems were then characterised using different analytical tools, i.e. X-ray photoelectron spectroscopy (XPS), X-ray-excited Auger electron spectroscopy (XE-AES), X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). These advanced microscopic and X-ray analytical methods were combined to gain complementary information concerning the composition and microstructure of the investigated composite systems. In addition, the characterisation of both systems by means of several investigation techniques provided a valuable insight into the potential features offered by sol–gel and ion implantation and enabled a fruitful comparison between these preparative routes. The influence of the different synthesis parameters on the final features of the composites is analysed and discussed.

Ultrathin film growth and spectroscopic characterization of VO x (0.8⩽ x⩽1.3) on Pt(1 1 1)

VO x ultrathin epitaxial films (0.8⩽ x⩽1.3) have been grown on Pt(1 1 1) by evaporating vanadium in a low and well-controlled water background (1×10 −7 Pa). X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and X-ray excited auger electron spectroscopy data strongly indicate that vanadium(II) in the predominant oxidation state. Angle-scanned photoelectron diffraction data are compatible with a single domain film, bearing a rock-salt VO structure and exposing the (1 1 1) plane. Such films evolve toward more oxidized species within hours, probably due to oxidation by residual water in the chamber.

γ-Al2O3 by Au 4f7/2-referenced XPS and XAES

Powder x-ray diffraction (XRD) defined γ-Al2O3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets.

Composition and Microstructure of Cobalt Oxide Thin Films Obtained from a Novel Cobalt(II) Precursor by Chemical Vapor Deposition

The present work reports the synthesis and the characterization of cobalt oxide thin films obtained by chemical vapor deposition (CVD) on indium tin oxide (ITO) substrates, using a cobalt(II) β-diketonate as precursor. The complex is characterized by electron impact mass spectrometry (EI-MS) and thermal analysis in order to investigate its decomposition pattern. The depositions are carried out in a cold wall reactor in the temperature range 350−500 °C at different oxygen pressures, to tailor film composition from CoO to Co3O4. The crystalline nanostructure is evidenced by X-ray diffraction (XRD), while the surface and in-depth chemical composition is studied by X-ray photoelectron (XPS) and X-ray excited auger electron spectroscopy (XE-AES). Atomic force microscopy (AFM) is employed to analyze the surface morphology of the films and its dependence on the synthesis conditions. Relevant results concerning the control of composition and microstructure of Co−O thin films are presented and discussed.

β-AlF3 by Au 4f7/2-referenced XPS and XAES

Powder x-ray diffraction (XRD) defined β-AlF3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets.

Sol-Gel and CVD Co3O4 Thin Films Characterized by XPS

The present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, and Co LVV) of nanocrystalline Co3O4 coatings. The samples were obtained by CVD and sol-gel routes. Co(dpm)2 (Hdpm = 2,2-6,6-tetramethyl-3,5-heptanedione) was chosen as CVD precursor thanks to its appreciable volatility, the absence of direct Co–C bonds and the presence of thermally labile Co–O moieties. The preparation of the sol-gel films was accomplished starting from methanolic solutions of Co(OCOCH3)2⋅4H2O due to the clean conversion of cobalt acetate into cobalt oxides. The obtained Co3O4 films were bluish-brown, homogenous, crack-free, and adhered well to the substrates. The microstructural analyses revealed the formation of single-phase nanostructured layers with average crystallite dimensions ranging between 15 and 26 nm.

LaCoO3 Nanopowders by XPS

Mixed oxide materials belonging to the perovskite family (ABO3, LaCoO3) have come under intense scrutiny for their possible applications in different scientific and technological fields, such as heterogeneous catalysis, oxygen sensors, solid oxide fuel cells and magnetic media. The growing interest in such mixed oxide systems relies on a detailed investigation of structure-properties relationships that can lead to the optimization of their performances with respect to different applications, e.g., catalysis, sensors, etc. Similar solid state devices would require high surface area thin films in order to optimize the full potential of these oxide materials; specifically, nanostructured systems with a high defect content (oxygen vacancies and local lattice disorder) are expected to show superior properties with respect to the conventional ones. The possibility to tailor these features as a function of the surface area and grain size appears thus as a powerful tool in order to optimize the material properties for functional applications. In particular the present investigation is focused on x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XE-AES) analysis of the main core levels (O 1s, Co 2p, Co LMM, La 3d, and La 4d) of LaCoO3 nanophasic powders obtained by combustion synthesis. The formation of LaCoO3 was ascertained by the position and shape of La 3d and Co 2p photopeaks.

Experimentally derived Auger transition probabilities in X-ray excited Auger electron spectroscopy (XAES)

The capability of Auger transition probabilities experimentally derived from X-ray excited Auger electron spectra in XPS were tested. The relative sensitivity factor (RSF) method has been employed in the quantification by AES (Electron excited Auger electron spectroscopy). However, the difference between experimentally derived RSF and theoretically calculated ones has been found in some reports. One of the great reason of the difference may be caused by the calculated values of the Auger transition yield which has been commonly employed without the consideration of the allotment of coupling scheme in the transition selected in the quantification, for instance, the allotment of each six coupling KL 1L 1, KL 1L 2, KL 1L 3, KL 2L 2, KL 2L 3, and KL 3L 3 in KLL transition. The employment of derived Auger transition probabilities reduce the difference between theoretically calculated RSF and experimentally derived one.

Surface characterization of polydimethylsiloxane treated pharmaceutical glass containers by X-ray-excited photo- and Auger electron spectroscopy.

The siliconization of pharmaceutical glass containers is an industrially frequently applied procedure. It is done by spreading an aqueous silicone oil emulsion film on the inner surface and successive heat curing treatment at temperatures above 300 degrees C for 10-30 min. It was often proposed that a covalent bonding of PDMS to the glass or branching of the linear PDMS occurs during heat treatment. The present study was performed for a detailed investigation of the glass and silicone (polydimethylsiloxane = PDMS) chemical state before and after heat-curing treatment and analysis of the bond nature. Combined X-ray excited photoelectron (XPS) and Auger electron spectroscopy as well as angle resolved XPS-measurements were used for analysis of the glass samples. The silicon surface atoms of the borosilicate container glass were transformed to a quartz-like compound whereas the former linear PDMS had a branched, two-dimensional structure after the heat curing treatment. It was concluded that the branching indicates the formation of new siloxane bonds to the glass surface via hydroxyl groups. Further evidence for the presence of bonded PDMS at the glass surface can be found in the valence band spectra of the siliconized and untreated samples. However, this bond could not be detected directly due to its very similar nature to the siloxane bonds of the glass matrix and the organosilicon backbone of PDMS. Due to the high variation of data from the siliconized samples it was concluded, that the silicone film is not homogeneous. Previously raised theories of reactions during heat-curing glass siliconization are supported by the XPS data of this investigation. Yet, the postulation of fixing or baking the silicone on the glass surface is only partially true since the bonded layer is very thin and most of the silicone originally on the surface after heat curing can be removed by suitable solvents. This fraction can therefore still interact with drug products being in contact to the siliconized container wall.

The structure of vanadia ultrathin films grown on TiO 2 (1 1 0) in an oxygen ambient

Vanadium oxide has been deposited on TiO 2 (1 1 0) by means of e-beam metal evaporation in an oxygen atmosphere at room temperature, following a procedure that has already been adopted by several groups. After an electronic structure characterisation based on XPS, X-ray excited Auger electron spectroscopy and valence band spectra, we have determined the lattice structure of ultrathin vanadia films approximately 5 and 18 monolayers thick by means of angle-scanned 2π photoelectron (XPD) measurements. While the electronic structure of the layers is close to that expected for V 2O 3, as judged from electron spectroscopies, XPD shows in a clear and direct way that the vanadia ultrathin films, instead of having the bulk-like corundum structure typical of V 2O 3, are characterised by a rutile lattice isomorphic to the substrate. This important difference with respect to vanadia ultrathin films grown on other substrates (e.g. Al 2O 3 (0 0 0 1) and Pd(1 1 1)), where the corundum structure is retained by the overlayer, could be a key to understanding the catalytic specificity and selectivity of titania-supported vanadia catalysts in many important chemical reactions.

Study of carbon nitride films deposited using a Hall-type ionsource

The Hall-type ion source operated with nitrogen has been used in twoways in the synthesis of carbon nitride films: by ion beam nitridation of agraphite target and by simultaneous deposition on a collector (silicon waferand nickel foil) of sputtered carbon atoms and nitrogen atoms from thesurrounding nitrogen plasma. We present Rutherford backscatteringspectroscopy, x-ray photoelectron spectroscopy and x-ray excited Augerelectron spectroscopy results on the carbon and nitrogen atom fraction andchemical bonding state in carbon nitride films. The C 1s XPS peak of a sampledeposited on silicon wafer was deconvoluted into three peaks at 284.7, 286.7and 288.8 eV. The peak at 286.7 eV by analogy with polymethacrylonitrile(C≡N, 286.74 eV) can be identified as C≡N, the peaks at284.7 and 288.8 eV as C-C and O=C-N, respectively. The N 1s peaks were alsodeconvoluted into three peaks at approximately 398.3, 400.5 and 402.6 eV.According to the N(E) CKVV spectra the surface samples contain an equal numberof sp2 and sp3 bonds of carbon atoms.

Photoelectron spectroscopic study of amorphous GaAsN films

Amorphous gallium–arsenic–nitrogen (a-GaAsN) thin films were deposited by sputtering a crystalline GaAs target with different mixtures of argon and nitrogen. X-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES) were employed to study the Ga and As core levels and the corresponding LMM Auger transitions of films with different N concentrations. Chemical information of these samples was obtained through the analysis of the Auger parameter, which is exempt from problems inherent in the interpretation of XPS and XAES shifts, revealing aspects associated with the composition of the a-GaAsN films. In particular, these experimental results show the preferential bonding of N to Ga atoms in the formation of N-rich amorphous GaAsN films.